When a moving web, such as paper, film, textile, foil or the like moves through a printing press or moves through processing machinery, the web often tends to wrinkle even though the web is usually supported by one or more rollers along its path of travel. Wrinkling of the web is generally undesirable as it usually impairs printing or processing of the web. Moreover, when the web is to be split into smaller constituent strips, wrinkles in the web may cause deviation in the strip size which may render the strips unsuitable for subsequent use.
To prevent web wrinkling, the web must be cross-stretched, that is to say, the web must be stretched perpendicular to the direction of web movement. Transverse or cross-stretching of the web has been accomplished in the past by use of a stretcher roller located along the path of web movement so as to be in contact with the web. Prior art stretcher rollers are typically configured of a rigid core which has an elastomeric covering. The covering is provided with either a single pair of spiral groove segments or a double pair of spiral groove segments of uniform depth and angle. The groove segments in the elastomeric cover of the roller create a plurality of ribs or lands which are separated from each other by one of the groove segments. As the web passes over the roller, the lands of the roller cover each exert a force on the web transverse to the direction of web movement to cross-stretch the web. The transverse stretching action of the roller lands keeps the web taut and wrinkle-free.
The disadvantage believed associated with present day stretcher rollers is that, although they are well suited for maintaining a single web taut, prior art stretcher rollers are generally not well suited for cross-stretching the individual strips which result when the web is slit. The cross-stretching force exerted by the lands of prior art stretcher/expander rollers tends to be uniform across the roller which does not readily facilitate simultaneous cross-stretching and separation of the constituent web strips following web slitting.